This invention relates to molds for forming a bundle of fibers into a unitary mass, and more particularly, to a mold forming a plurality of fibers into a mass with relatively little spatial distortion.
Molds are conventionally used to form a fiber bundle into a unitary mass having a cross-sectional shape corresponding to the shape of the mold. For example, U.S. Pat. No. 3,904,343 to Scott, Jr. discloses a mold for forming a bundle of glass fibers into a hexagonal mass. A conventional hexagonal mold 10 of the type shown in the patent to Scott, Jr. is shown in FIG. 1. The mold 10 includes an angle block 12 having a first hexagonal surface 14 and an angle block 16 having a second hexagonal surface 18. The angle block 16 moves laterally in the channel member 14 responsive to rotation of a jack screw 20. A hexagonal bundle 22 of fibers is placed in the bottom portion of the mold formed by the channel member 14 and angle block 16. Three upper angle blocks 30, 32, 34, each of which has a respective hexagonal surface 36, 38, 40, is then placed on the bundle 22. The upper angle blocks 30, 32, 34 move downwardly to compress the bundle 22 during the molding operation. Also, the angle block 16 may move laterally to compress the bundle 22. It will be apparent that the angle blocks 30, 32, 34 move not only relative to the channel member 12, but also relative to each other. Under these circumstances, the fiber bundle 22 will accurately assume a hexagonal configuration only if the hexagonal symmetry of the angle blocks 30, 32, 34 is maintained while the blocks move relative to each other. However, since there is no mechanism to ensure that symmetry is maintained, the prior art mold 10 may be incapable of forming hexagonal fiber masses with sufficient accuracy.
There is therefore a need for a mold that can accurately form a bundle of fibers into a hexagonal mass without spatial distortion.
According to one aspect of the invention, a mold is specially adapted for forming a plurality of fibers into a bundle having a hexagonal cross-sectional shape. The mold includes a base and a unitary cover. The base has an upwardly facing lower cavity defined by a bottom surface and a pair of side walls. The side walls extend from opposite sides of the bottom surface upwardly away from each other at approximately 120 degrees with respect to the bottom surface. As a result, the bottom surface and side walls together define one-half of a hexagon. The unitary cover has a downwardly facing upper cavity defined by a top surface and a pair of side walls. The side walls extend from opposite sides of the top surface downwardly away from each other at approximately 120 degrees with respect to the top surface. As a result, the top surface and side walls together also define one-half of a hexagon. The mold base is adapted to receive the mold cover with the upper and lower cavities facing each other so that the upper and lower cavities define a hexagonal mold cavity. Since the cover is unitary rather than formed by a plurality of sections that are movable relative to each other, the mold cavity accurately maintains a hexagonal shape.
The mold may be used to mold a plurality of single fibers into a multiple fiber preform having a cross-sectional shape of a hexagon by placing a plurality of single fibers into the base before placing the unitary cover over the mold base. During the molding process, the mold base is preferably forced against the mold cover to compress the fibers in the mold cavity. The fibers may also be heated while they are being compressed in the mold cavity.
The hexagonal multiple fiber preform formed using the mold may be used for a variety of purposes. For example, a plurality of hexagonal preforms may be molded into a fiber block by drawing the hexagonal multiple flow preform into a hexagonal multiple fiber, and then placing a plurality of hexagonal multiple fibers in a mold cavity preferably along with multiple fibers having a cross-sectional shape of a half-hexagon. The hexagon and half-hexagon multiple fibers are arranged in the mold so that the half-hexagon multiple fibers fill respective spaces formed between adjacent hexagon multiple fibers and the bottom of the mold base. A cover is then placed over the mold cavity and the multiple fibers are molded into a unity of fiber blocks.
The fiber block can be sliced into a thin sheet and used for such purposes as a spacer for a flat panel display and a microchannel plate for a field emission display. A flat panel display spacer is formed by placing single fibers in the hexagonal mold that have an inner core and an outer cladding that is selectively removable from the inner core. One face of a thin sheet sliced from the fiber block is attached to either a baseplate or a faceplate of the flat panel display. The outer cladding is then removed from the inner core, such as by etching, thereby leaving strands of material formed from the inner core attached to the baseplate or the faceplate of the flat panel display. The other face of the sheet is then attached to the other of the baseplate or faceplate so that the strands of core material space the baseplate and faceplate apart from each other.
A microchannel plate for a field emission display is formed by placing single fibers in the hexagonal mold that have an inner core that is selectively removable from the outer cladding. A thin sheet sliced from the fiber block is mounted within a space formed between the baseplate and the faceplate of the field emission display. After mounting the slice of fiber block in the display, the inner core is selectively removed from the outer cladding by a suitable procedure, such as by etching. As a result, a sheet having a large number of channels corresponding to the outer claddings is formed between the baseplate and the faceplate of the field emission display.